Messages in this thread Patch in this message | | | Date | Mon, 01 Oct 2007 22:10:03 +0200 | From | Eric Dumazet <> | Subject | Re: 2.6.21 -> 2.6.22 & 2.6.23-rc8 performance regression |
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So maybe the following patch is necessary...
I believe IPV6 & DCCP are immune to this problem.
Thanks again Denys for spotting this.
Eric
[PATCH] TCP : secure_tcp_sequence_number() should not use a too fast clock
TCP V4 sequence numbers are 32bits, and RFC 793 assumed a 250 KHz clock. In order to follow network speed increase, we can use a faster clock, but we should limit this clock so that the delay between two rollovers is greater than MSL (TCP Maximum Segment Lifetime : 2 minutes)
Choosing a 64 nsec clock should be OK, since the rollovers occur every 274 seconds.
Problem spotted by Denys Fedoryshchenko
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
--- linux-2.6.22/drivers/char/random.c 2007-10-01 10:18:42.000000000 +0200 +++ linux-2.6.22-ed/drivers/char/random.c 2007-10-01 21:47:58.000000000 +0200 @@ -1550,11 +1550,13 @@ __u32 secure_tcp_sequence_number(__be32 * As close as possible to RFC 793, which * suggests using a 250 kHz clock. * Further reading shows this assumes 2 Mb/s networks. - * For 10 Gb/s Ethernet, a 1 GHz clock is appropriate. - * That's funny, Linux has one built in! Use it! - * (Networks are faster now - should this be increased?) + * For 10 Mb/s Ethernet, a 1 MHz clock is appropriate. + * For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but + * we also need to limit the resolution so that the u32 seq + * overlaps less than one time per MSL (2 minutes). + * Choosing a clock of 64 ns period is OK. (period of 274 s) */ - seq += ktime_get_real().tv64; + seq += ktime_get_real().tv64 >> 6; #if 0 printk("init_seq(%lx, %lx, %d, %d) = %d\n", saddr, daddr, sport, dport, seq); | |